In communications receivers, analog processing equipment, and the like, it is often necessary to perform a multiplication of two signals x(t) and y(t) to yield an output signal wave form which represents the product thereof. When the wave forms of x(t) and y(t) are relatively slowly varying, the power spectra thereof have no significant components at relatively high frequencies. In such cases, conventional multiplier circuits are available which can provide the desired product wave forms without difficulty. However, a problem arises when both x(t) and y(t) vary in such a manner that the power spectra thereof have components that are of relatively high frequencies, e.g., frequencies of greater than 100 kHz, for example. Present techniques for dealing with such high frequency component problems have proved unsatisfactory in producing accurately the desired wave form.
One approach which has been utilized for such purpose is applicable when either x(t) or y(t) has special amplitude characteristics. Specifically, for example, if x(t) is such that it assumes only two amplitude states, .+-.V as defined by the expression ##EQU1## a bridge multiplier circuit using diode gates has been utilized and permits almost arbitrarily large bandwidths for both x(t) and y(t) to be present in producing the product wave form. Such an approach would also be useful even if x(t) is, for example, of the form: EQU x(t) = V cos[.omega.t+.phi.(t)],
where V is a constant amplitude and all of the variations of x(t) from a pure sinusoid are conveyed by the phase modulation term .phi.(t). A gated-diode bridge multiplier circuit can be used with such a wave form because the gates open and close coincidentally with the zero-crossings of x(t) which zero-crossings essentially carry all of the necessary information concerning the phase mudulation term .phi.(t). Although such bridge circuitry permits relatively wide bandwidths for the x(t) and y(t) input signals, it is limited to multiplying signals at least one of which has a constant amplitude.
Another approach which has been suggested also involves a bridge circuit using PIN-diodes. The PIN-diode bridge circuit permits the amplitudes of both x(t) and y(t) to vary. However, because of transit-time limitations thereof, one of the inputs to the multiplier circuitry must have its spectral content (i.e., its frequency components) limited to frequencies below about 100 kHz. Such a limitation on the use thereof prevents such a bridge circuit from being applicable in many analog processing systems wherein the frequency components are significantly larger than 100 kHz.